I've talked to a guy that has a v8 swapped 940, but he doesn't have a ford 8.8 rear axle, but instead an upgraded volvo axle with 4.10 gears. Where can I find a 4.10 posi for a Volvo rear axle, and how much of a cost difference would it be versus getting an entire ford 8.8?

Your best bet for a 4:10 R&P is to post in the wanted section, somebody most likely has a set they will sell. Many Volvos had G80 lockers in them, even install Detroit Truetrac units. Another option for open diffs is to use a Richmond/PowerTrax locker, but they are fairly noisy and the locking can be quite brutal if you don't know what you are doing.

As far as the 8.8, it could be relatively cheap or ridiculously expensive. They require some modification to fit, and if you can do it all yourself, this would be the way to go. If you have to get the housing cut and brackets moved at a shop, it could cost you dearly. There are plenty of threads on how to do this modification in this forum, so do yourself a favor and read up on it first.

Are you running a V8? What tire size in the rear? Manual or Auto? 4.10 is kind of steep. 3.73 with a 0.73od and stock sized tires is pretty buzzy for freeway driving as well. 3.53 or 3.31 would be nice for a lot of freeway driving.
You can probably find an entire axle with 4.10 gears for the same price as a set of used gears.
Trutrac 588 is the one you want for the rear, if you want to go that route. https://www.summitracing.com/parts/dtl-912a588
I'd avoid a G80 as it's just crushing disappointment if you actually want something that is smooth.

Are you running a V8? What tire size in the rear? Manual or Auto? 4.10 is kind of steep. 3.73 with a 0.73od and stock sized tires is pretty buzzy for freeway driving as well. 3.53 or 3.31 would be nice for a lot of freeway driving.
You can probably find an entire axle with 4.10 gears for the same price as a set of used gears.
Trutrac 588 is the one you want for the rear, if you want to go that route. https://www.summitracing.com/parts/dtl-912a588
I'd avoid a G80 as it's just crushing disappointment if you actually want something that is smooth.

I wasn't particularly meaning a 4.10, I was just wondering where I could acquire an upgrade for the stock rear axle.

Are you running a V8? What tire size in the rear? Manual or Auto? 4.10 is kind of steep. 3.73 with a 0.73od and stock sized tires is pretty buzzy for freeway driving as well. 3.53 or 3.31 would be nice for a lot of freeway driving.
You can probably find an entire axle with 4.10 gears for the same price as a set of used gears.
Trutrac 588 is the one you want for the rear, if you want to go that route. https://www.summitracing.com/parts/dtl-912a588
I'd avoid a G80 as it's just crushing disappointment if you actually want something that is smooth.